Non-petroleum-based alternative feedstocks for the production of organic materials (e.g., sugars, linear hydrocarbons, lipids) potentially offer the chemical industry substantial economic and environmental benefit by supplementing or displacing petroleum products in chemical and energy markets. For example, the extraction of sugars (e.g., glucose and xylose) from lignocellulose biomass during the pretreatment stage is a focused research and development effort by the U.S. Department of Energy and by private industry for production of biofuels, bio-based products, and biochemicals. Bioprocess pretreatment technologies generally produce a low titer of target organic products, which requires significant downstream product separations to purify the target materials from complex mixtures, and dewatering to concentrate the target materials to useful concentrations. A technoeconomic assessment of the fermentation of sugars from corn stover to produce cellulosic ethanol found that one third of the production costs came from the pretreatment stage. The separation and concentration of ethanol, which is limited by the sugar titer, consumed half of the total process energy budget.
For example, sugar concentration in most pretreated lignocellulose hydrolysate (i.e., the liquid fraction of dissolved sugar molecules in a pretreatment slurry) is approximately 2 to 10 percent by weight (wt %). Removal of water from the hydrolysate to increase the sugar concentration is expensive. In another example, phototrophic and heterotrophic algae are used to produce lipids for biofuel production. The ultimate lipid content in the algal slurries may be less than 1 wt %. Removal of water from the lipid can use more energy than is contained in the lipid product.
Magnetic nanoparticles of various types have been used in biomass processing. For example, acid-functionalized nanomaterials reportedly were useful for the pretreatment and hydrolysis of lignocellulosic biomass (L. Pena, M. Ikenberry, B. Ware, K. L. Hohn, D. Boyle, X. S. Sun, and D. Wang, “Cellobiose Hydrolysis Using Acid-functionalized Nanoparticles,” Biotechnology and Bioprocess Engineering, 2011; 16(6):1214-1222). In this study, cobalt spinel ferrite (CoFe2O4) nanoparticles were surface treated with silica and functionalized to varying degrees with acid groups. The functionalized nanoparticles were utilized as acidic processing aids to hydrolyze lignocellulose, and the particles were then magnetically separated from the reaction medium and reused. Although cellobiose hydrolysis was observed, nanoparticle aggregation occurred, the result of ferromagnetic behavior of silica-coated metal oxide nanoparticles (large XRD peaks were observed, and hydrolysis degraded with cycle count). The acidic nanoparticles in this study were utilized as a hydrolyzing agent, and the resulting sugars were isolated and concentrated by conventional means. Magnetic separation processes also have been used in solid waste disposal and recycling operations.
Flotation has been used in separation processes, as well. Such separations often depend on density or wettability differences to separate product components. However, the use of sorbents, which are surface treated to selectively capture sugar or other targeted organic products, and capable of being separated from complex process streams by flotation has not been reported.
The passivation and functionalization of particles has been addressed over the years by many different techniques and chemical efforts. Functional magnetic nanoparticles that can be separated from a fluid using a magnetic field have been described in, e.g., in U.S. Pat. No. 7,795,041 to Hatton et al., which is incorporated herein by reference in its entirety. The magnetic nanoparticles described by Hatton et al. were directly embedded into and non-covalently bound with a polymer, and lacked chemical stability, which led to the loss of magnetization of the particles over time and particle dissolution under conditions of the process environment.
Others have coated the surface of particles to modify the physical or chemical properties of the particle surfaces. Sorption, ion exchange or binding, and covalent bonding techniques have conventionally been used to coat particulate surfaces. Sorption and ion exchange require the surface to have the appropriate chemical characteristics, and reactions that enable covalent bonding to particle surfaces generally involve reactions with surface-bound hydroxyl groups. U.S. Pat. No. 7,524,630 to Tan et al., which is incorporated herein by reference in its entirely, describes nanoparticles having a core/shell structure with a magnetic core and silicon oxide shell surface-functionalized with biologically active molecules such as antibodies and nucleotides. The nanoparticles of U.S. Pat. No. 7,524,630 reportedly are useful to label cells, to detect and isolate nucleic acid molecules having specific nucleotide sequences, and to separate a mixture of different nucleic acid molecules. More specifically, U.S. Pat. No. 7,524,630 discloses a pre-formed silica surface being conjugated with at least one functional group comprising an oligonucleotide in the form of a molecular beacon, in which the oligonucleotide comprises a single-stranded loop structure comprising a nucleic acid sequence of interest. However, biologically active molecules such as nucleotides or antibodies conjugated to the particle surface are rapidly consumed or degraded by deleterious compounds present in the biomass-process environment, and thus cannot be used for sorption of targeted organic materials in such processes.
U.S. Pat. No. 6,548,264 to Tan et al., which is incorporated herein by reference in its entirety, discloses silica-coated nanoparticles and a process for producing silica-coated nanoparticles. Silica-coated nanoparticles in accordance with U.S. Pat. No. 6,548,264 are prepared by precipitating nano-sized cores from reagents dissolved in the aqueous compartment of a water-in-oil microemulsion. A reactive silicate is added to coat the cores with silica. The method employs a microemulsion, i.e., isotropic and thermodynamically stable single-phase system, to produce nanoparticle cores of a predetermined, very uniform size and shape. The coated nanoparticles reportedly can be customized for a particular application by derivatizing various chemical groups onto the pre-formed silica coating. However, the microemulsion synthesis described in U.S. Pat. No. 6,548,264 is cumbersome, cannot be readily scaled up, and requires purification of the particles from the surfactant employed to create the microemulsion.
Others have found similar methods of nanoparticle functionalization to be useful for isolation of biological material such as nucleic acids, medical screening, monitoring for chemotherapy, treatment responses, cancer recurrence or the like. Typically these coatings are thin surface treatments on metal oxide cores, which afford dispersion compatibility and, for the best available technology, control particulate aggregation, but cannot prevent ion migration from reactive (e.g., metal) particles or affect ultimate sorption properties.
There is an ongoing need for alternative materials and methods for separating target organic products such as sugars, lipids, and hydrocarbons, from fluids such as bioprocess streams. The compositions and methods described herein address this ongoing need.